Signal-translating circuit



July 9, 1940. H.'A. WHEELER SIGNAL-TRANSLATING CIRCUIT Filled March 28,1959 Patented July 9, 1940 PATENT OFFICE 2,206,989 SIGNAL-rmsmmc onwm'rHarold A. Wheeler, Great Neck, N. Y., assig-nor to HazeltineCorporation, a corporation of Delaware Application March 28,

11 Claims.

This invention relates to signal-translating circuits and. while ofgeneralapplication, it is of particular utility in the line-scanningoutput circuits of cathode-ray tube television apparatus.

In certain signal-translating systems', it is necessary to transform asignal of any given frequency within a wide range of frequencies or totrans-form a signal having a Wide range of component frequencies, andthe transformer circuits utilized for such purposes are frequently suchas to produce an undesirable irregularity in the frequency-responsecharacteristic of the system at one or more particular frequencieswithin the operating range. Further, an undesired transient effect maybe caused if the transformed signal comprises a wide range of componentfrequencies.

Thus, for instance, in a television receiver comprising anelectromagnetic scanning circuit, it is desirable to translate a currenthaving a sawtooth wave form which, in effect, comprises componentfrequencies of a very Wide frequency range. Furthermore, it isfrequently desirable to provide the scanning current to the scanningWinding of the system from a vacuum tube through a step-downtransformer. In such a system, the circuit comprising thescanning-Winding inherently comprises appreciable shunt capacitancewhich resonates with the associated circuit inductances and therebytends to cause irregularities in the frequency-response characteristicof the circuit at one or more particular frequencies with the attendantundesirable effects mentioned above. Also, inherent capacitance couplingthe transformer windings of such a system in opposition to theirtransformer coupling may cause a similar undesirable response but inopposite sense. Similarly, in a television receiver compris-ing anelectrostatic scanning circuit, a step-up transformer is frequentlyutilized between the last vacuum tube in the scanning-signal translatingchannel and the scanning plates of the cathode-ray tube. In such acircuit also, capacitance across the output electrode of the tube, aswell as the inherent capacitive coupling in opposition to thetransformer coupling, may cause undesirable responses similar to thosementioned above.

It is an object of the invention, therefore, to provide asignal-translating circuit of the type under discussion which eliminatesone or more of the above-mentioned disadvantages of systems of the priorart.

It is a further object of the invention to provide a signal-translatingcircuit comprising a stepdown transformer for translating scanningcurrents in a television system utilizing electromagnetic scanning, inwhich the detrimental effect of capacitance across the scanning windingsof the system is substantially eliminated.

It is still another object of the invention to provide asignal-translating circuit comprising 1939, Serial N0. 264,525

a voltage-changing transformer for translating scanning currents in atelevision system, in which the detrimental effect of capacitancecoupling in opposition to the transformer coupling is substantiallyeliminated.

In accordance with the invention, a signaltranslating circuit forpassing a signal comprising a band of frequencies comprises atransformer having closely-coupled primary and secondary windings ofsubstantially different inductances, a terminal circuit connected withthe one of the windings of lower inductance, capacitance effectivelyacross the terminal circuit, and capacitance effectively coupling thewindings in opposition to their transformer coupling. The capacitancesof such a system resonate with resultant inductance of the transformerand of the terminal circuit at a particular frequency within the bandand, in accordance with the invention, the capacitances are relativelyso proportioned with respect to the inductances of the system assubstantially to balance out any irregularity in the couplingcharacteristic of the translating circuit between said terminal circuitand said winding of greater inductance at frequencies in the vicinity ofthe said particular frequency of undesired resonance. Either of theabove-mentioned capacitances may be comprised, in whole or in part, ofinherent circuit capacitance of the signal-translating circuit, oreither of the above-mentioned capacitances may be comprised, in whole orin part, of capacitance means added to the circuit to balance out theundesired irregularities in accordance with the invention.

Also in accordance with a preferred embodiment of the invention, thetransformer is a stepdown transformer utilized to couple a vacuum tubeto the scanning windings of a television signal receiver utilizingelectromagnetic scanning. In accordance with another preferredembodiment of the invention, the transformer is a stepup transformerutilized to couple a vacuum tube to the scanning plates of a televisionreceiver utilizing electrostatic scanning, preferably by means of abalanced circuit.

As used in this specification, the term closelycoupled refers to acoefficient of coupling of a higher order of magnitude than that betweenaircore transformer windings or radio-frequency transformers wherein thecoeiiicient of coupling usually does not exceed a few per cent. In otherwords, in a transformer having closely-coupled primary and secondarywindings according to this invention, the windings are as close asphysical factors will permit and have a coefficient of coupling of notless than per cent and usually more, such as upwards of 90 per cent.

For a better understanding of the invention, together with other andfurther objects thereof,

reference is had to the following,v specication taken in connection withthe accompanying drawing, and its scope will be pointed out in theappended claims.

Fig. 1 of the drawing is a circuit diagram, partly schematic, of acomplete television signal receiver comprising an electromagneticline-scanning circuit embodying the invention; Fig. 2 is an electricalequivalent circuit diagram of a portion of the scanning-signaltranslating channel of Fig. 1; Figs. 3a and 3b are characteristic curvesutilized to describe certain operating characteristics of the circuit ofFig. 2; Fig. 4 is a modification of the circuit of Fig. 2 utilized forobtaining relationships for proportioning thecircuit elements of Fig. 1in accordance with the invention; Fig. 5a illustrates the load voltageof a prior art system similar to that of Fig. 1; Fig. 5b illustrates theload voltage of the system of Fig. 1; Fig. 6 illustrates a modificationof the circuit of Fig. 1 to .provide a balanced signal-translatingcircuit; Fig. 7 illustrates a modification of the signal-translatingcircuit of Fig. l utilizing a transformer comprising separate primaryand secondary windings; while Fig. 8 illustrates a modification of thecircuit of Fig. 6 as utilized in the scanning-signal translating channelof a television receiver utilizing electrostatic scanning.

Referring now more particularly to Fig. 1 ofy the drawing, the Vsystemthere illustrated comprises a television receiver of the superheterodynetype including an antenna system III, I I connected to a radio-frequencyamplifier I2 to which are connected in cascade, in the order named, anoscillator-modulator i3, an intermediate-frequency amplier Ill, adetector I5, a video-frequency amplifier I 6, and an image-reproducingdevice I l, for example, a cathoderay receiver tube. A pulse-voltageline-frequency generator I8 and a field-frequency generator I 9 arecoupled to the output circuit of detector I5 and to the sets ofdeiiecting windings 2i), 28 and 2l, 2i, respectively, the line-frequencygenerator I8 being coupled to linedeiiecting windings 20, 20 through arepeated 22, presently to be described. The stages or units I-IQ,inclusive, may allbe of conventional well-known construction so thatdetailed illustration and description thereof are deemed unnecessaryherein. Y

Referring briefly, however, to the general operation of the systemdescribed above, television signals intercepted by antenna circuit I0,Ii are selected and amplified in radio-frequency amplifier I2 andcoupled to the oscillator-modulator I3, wherein they are converted intointermediatefrequency signals which, in turn, are selectively amplifiedin the intermediate-frequency amplifier Ill and delivered to thedetector I5. 'I'he modulation components of the signal are derived bythe detector I 5 and the video-frequency signals are supplied to thevideo-frequency amplifier I 6,

wherein they are further amplified and fromwhich they are supplied inthe usual manner to a brilliancy-control electrode of theimage-reproducing device I'I. Synchmnizing signals are supplied fromdetector I5 to the control elements of the generators I 8 and I9. Theintensity of the scanning ray Aof device il is thus modulated orcontrolled in accordance with the video-frequency voltages impressedupon its control electrode in the usual manner. Scanning waves aregenerated in the line-frequency and field-frequency generators I8, 22,and I8, which are controlled by the synchronizing voltages supplied fromdetector I5, and applied to the scanning elements of theimage-reproducing device I1 to produce electromagnetic scanning elds.thereby to deect the scanning ray in two directions normal to each otherso as to trace al rectilinear scanning pattern on the screen and toreconstruct the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1embodying the present invention, there is provided a saw-tooth currentgenerator including a vacuum tube 25 coupled to the output circuit ofpulse-voltage generator I8. Therer are included in the output circuit oftube 25 a parallel-connected condenser 26 and resistor 21 effective todevelop from the pulse current output of tube 25 a saw-tooth voltagewave, in a manner well understood in the art. This sawtooth voltage iscoupled to the input circuit of a vacuum tube 28 through a couplingcondenser 29 in order to provide a saw-tooth current through scanningwindings 20, 20 from the output circuit of tube 28, the output circuitof tube 28 being coupled to the scanningwindings 20, 28 through astep-down autotransformer including windings 80, 3I The output circuitof vacuum tube 28 may have appreciable inherent capacitances,represented in the drawing by dotted-line condenser 32 across the entirecircuit and dotted-line condensers 3l and 38 across the windings 3i and38, respectively. These inherent capacitances tend to disturb theuniformity of variation of the current through scanning coils 20, 2li,which is detrimental during the trace intervals of the scanning cycle.In order to compensate for the eect of capacitance 32, therefore, therean inductance 33 connected in series with resistor 34 andparallel-connected condenser 26 and resistor 2l in the output circuit ofvacuum tube 25.

In considering the characteristic of the circuit 22 of Fig. 1, it willbe seen that any inherent capacitance 3I across winding 38 resonateswith the associated circuit inductances at a particular frequencyand\that any inherent capacitance 38 across winding 3i also resonateswith the associated circuit inductances at a particular frequency. Thesetwo frequencies are, in general, different from each other and from themain resonant frequency of the output circuit of tube 28 as a whole andthereby tend to cause one or more irregularities in the couplingcharacteristic between generator I8 and scanning windings 20, 2li atfrequencies at which such irregularities are not corrected by inductance33 and, therefore, are detrimental. Therefore, in accordance with theinvention, either or both of supplemental condensers 39 and #I0 areincluded in the circuit of Fig. l in parallel with capacitances 37 and38, respectively, to balance out any irregularities in the couplingcharacteristics of the system at frequencies in the vicinity of anundesired resonance.

Reference is now made to Figs. 2-5b, inclusive, in order to show themanner in which the circuit of Fig. 1 is proportioned in order tobalance out such undesired resonance. In Fig. 2 there is shown a circuitwhich is the electrical equivalent of a portion of the circuit of Fig.l. The transformer 30, 3l of Fig. l may be resolved into the uncoupledinductance components La, Lb, and Lm of Fig. 2 in a manner Wellunderstood in the art, in which La-i-Lm is the total primary inductanceand Lb-I-Lm is the total secondary inductance. In a closely-coupledtransformer, the component Lb may be negative. Windings 20, 28

are represented in the circuit of Fig. 2 by the single inductance Lc,while capacitance Cb replaces capacitances 38 and 20 and capacitance ispreferably provided ascenso Cm replaces capacitances 31 and 33 oi'Fig. 1. Capacitance 32 of Fig. 1 is replaced by capacitance Cs in thecircuit of Fig. 2.

'I'he general coupling characteristics of the equivalent circuit of Fig.2 are illustrated by the characteristic curves of Figs. 3a and 3b. Undermost conditions, the transformer 30.' 3| and its associated inductancesand capacitances has a main or fundamental resonant frequency, producinga major peak in the response characteristic, at a frequency f1, whilethe leakage inductance of transformer 30, 3| resonating with theassociated circuit capacitances produces a minor peak at a frequency fz.The major peak alone is shown by the full-line curve of Fig. 3a and is aresponse characteristic which may be corrected by the coupling elements33, 33. 26, and 21 to procure the desired over-all responsecharacteristic from the system. The minor peak X of Fig. 3a is alsopresent if the capacitance Cb in the secondary or low inductance circuitof Fig. 2- is relatively too great. On the other hand, the minor valleyY is present ii' the capacitance Cm of Fig. 2 is relatively too great.If the primary or high inductance side of the circuit of Fig. 2, thatis, the side comprising terminals 3, is connected with an externalcircuit of very i low impedance, the main resonance oi' the transformercoupling system is destroyed and only the peak or valley caused by thespurious resonance of the leakage inductance remains, this circuitcharacteristic being illustrated in Fig. 3b. v It is, therefore, thepurpose of the present invention to proportion the circuit of Fig. 2 insuch manner as substantially to eliminate the minor peak X or valley Y.

lf the circuit of Fig. 2 is to balance out the above-mentioned undesiredirregularity (peak or valley) in the coupling characteristic, it isnecessary to obtain the eiect of no capacitance current flowing from thejunction of capacitances Cm and Cb through either of the inductances Laand la of Fig. 2. That is, equal capacitive currents should iiow intothe junction of Cm and Cb through one of these capacitances and outthrough the other. In order to derive an expression for proportioningthe circuit of Fig. 2 to meet this condition, it is to be compared withthat of Fig. 4 where corresponding elements are given identicalreference numerals. The condition set forth above is met if theterminals l and 2 of the circuit of Fig. 4 are at the same potential, asdriven from terminals 3 and 3, so that no current would flow in aconnection between these terminals. The following equations are derivedon this basis, in which Ei represents the voltage across condenser Caand Ea represents the voltage across either inductance Le or condenserCb under the condition assumed:

from Equations l and 2 the following relation is derived:

A circuit in accordance with that 'of Fig. l and proportioned inaccordance with Equation 3 is effective to balance out an undesiredirregularity in the coupling characteristics of the system, because thecapacitances Cb and Cm, representing condensers 31, 38, 33, and di) arethen effective merely to supplement the capacitance C., or condenser 32,across the entire output circuit of tube 23.

The load voltage across scanning windings 20, 20 of Fig. 1, in a circuitin which the undesired irregularity is not balanced out, is illus,-trated by the curve of Fig. 5a. 'I'he effect of the undesired resonanceis to produce a transient in tlie load voltage, especially during theearly part of the trace interval and immediately following the retraceinterval. If the circuit of Fig. 1 is proportioned in accordance withEquation 3, however, the load voltage across scanning windings 20, 20 isin accordance with that illustrated by the curve of Fig. 5b, from which,it is seen, the undesired transient has been eliminated. This'test maybe used for adjusting supplemental condensers 39, 40 to secure thedesired balance.

The output circuit of tube 28 of Fig. 1 may be balanced with respect toground. In Fig. 6 there isillustrated a circuit corresponding to aportion il Fig. 1 comprising such a balanced network. Similar circuitelements are given identical reference numerals in the two figures. Iheprincipal change which is made in the circuit of Fig. 6 is that each ofthe elements 30, 31, and 33 of Fig. 1 has been divided into two elements30'., 31', and 33', respectively, in Fig. 6, the corresponding elementsbeing connected in a balanced relation with respect to winding 3l of thetransformer. f

Furthermore, it will be understood that, while an autotransformer hasbeen shown in the circuit of Fig. 1, the invention is equally applicableto a circuit comprising a transformer having separate primary andsecondary windings, such a circuit being shown in Fig. 7 wherecorresponding circuit elements have reference numerals identical tothose of Fig. 1, except the high inductance transformer primary windingwhich is indicated at 30".

It will also be understood that the `invention is equally applicable toa circuit comprising a step-up transformer utilized to couple a vacuumtube to the scanning plates of a television receiver utilizingelectrostatic scanning. In Fig. 8 there is illustrated a circuitutilized for this purpose, which is otherwise equivalent to that of Fig.6. The input and output terminals of the circuit of Fig. 6 have beenreversed in the cifcuit of Fig. 8 and the capacitance 32 of Fig. 8 maybe comprised, in Whole or in part, of the capacitance of the scanningplates 50 of the image-reproducing device `l1. Winding 3| of Fig. 8 iscoupled to the output terminals of a balanced saw-tooth voltagegenerator 5| of high impedance and either or both of capacitances 39 and40 may be comprised, in whole or in part, of the output capacitance ofthe generator and the inherent capacitance of the transformer. In Fig.8, there is no inductance corresponding to the scanning inductance Le ofFig. 2, so the relation of Equation 3 above is simplified by giving Lean infinite value:

The capacitance 37 and 33 or 31" and 33' in Figs. 1, 6, 7, and 8providescoupling 'between the primary and secondary circuits of thetransformer, together with its directly associated cv!- pacitances orother reactance elements. such as the load inductance 20, -20, has aresonant frquency which is usually much higher than the main resonantfrequency of the system.. It is this spurious resonant frequency,denoted fr in Fig. 3, at which the resonance of the lower inductancecircuit tends to cause an irregularity in the frequency-responsecharacteristics or a damped transient oscillation. The resonance of thiscircuit is made ineffective by balancing the circuit capacitances and,if necessary, other impedances in the relations described above. Theeffect of balancing the capacitances associated with the winding 3i isto nullify the coupling of the transformer at the frequency where thisspurious resonance would occur. The coupling 'the appended claims tocover all such changes and modications as fall within the true spiritand scope of the invention. y

What is claimed is:

1. A signal-translating circuit for passing a signal comprising. a bandof frequencies, said circuit comprising, a transformer havingcloselycoupled primary and secondary windings of substantially dierentinductances, a terminal circuit connected with the one of said windingsof lower inductance, capacitance effectively across said terminalcircuit, and capacitance effectively coupling said windings inopposition to their transformer coupling, said capacitances resonatingwith the resultant inductance of said ,transformer at a frequency withinsaid band, at

which vsuch resonance is undesired, and said capacitances beingrelatively so proportioned with lower inductance. capacitanceeffectively across said terminal circuit, and capacitance eifectivelycoupling said windings in opposition` to their transformer coupling,said capacitances resonating with the resultant inductance of saidtransformer and said terminal circuit at a frequency within said band atwhich such resonance is undesired, and said capacitances beingrelatively so proportioned with respect to said inductances assubstantially to balance out any irregularity inthe couplingcharacteristics between said terminal circuit and said winding ofgreater inductance at frequencies in the vicinity of said frequency ofAundesired resonance.,

3. A signal-translating circuit for passing a signal comprising a bandof frequencies, said circuit comprising, a transformer havingcloselycoupled primary and secondary windings of substantially dierenuinductances, a terminal circuit connected with the one of 'said windingsof lower-inductance, capacitance consisting at least partially ofinherent circuit capacitance eiectively/across said terminal circuit,and capacitance effectively coupling said windings in opposition totheir transformer coupling, said capacitances resonating with theresultant inductance of said transformer and said terminalmcircuit at afrequency within said band at which such resonance is undesired,and-said capacitances being relatively so proportioned with respect tosaid inductances as substantially to balance out any irregularity in thecoupling characteristics between said terminal circuit and said windingof greater inductance at frequencies in the vicinity of said frequencyof undesired resonance.

4. A signal-translating circuit for passing a signal comprising a bandof frequencies, said cir- .cuit comprising, a transformer havingcloselycoupled primary and secondary windings of substantially diierentinductances, a terminal circuit connected with the one of said windingsof lower inductance, capacitance effectively across said terminalcircuit, and capacitance consisting at least partially of inherentcircuit capacitance eiectively coupling said windings in opposition totheir transformer couplingVsaid. capacitances resonating with theresultant inductance of said transformer and said terminal circuit at afrequency within said band at which such resonance is undesired, andsaid capacitancesbeingrelatively so proportioned with respect to saidinductances as substantially to balance out any irregularity in terminalcircuit, capacitance consisting of inherent circuit capacitanceeffectively coupling said windings in opposition to their transformercoupling, said capacitances resonating with the resultant inductance ofsaid transformer and said terminal circuit at a frequency within saidband at which such resonance is undesired, and additional capacitanceeffectively in parallel with one of said mst-mentioned capacitances andof such value as substantially to balance out any irregularity in thecoupling characteristics between said terminal circuit and said windingof greater inu ascenso ductance at frequencies in the vicinity of saidparticular frequency of undesired resonance.

6. A signal-translating circuit for passing a signal comprising a bandof frequencies, said circuit comprising, a transformer havingclosely-coupled prima-ry and secondary windings of substantiallydifferent inductances, a terminal circuit connected with the one of saidwindings of Tower inductance, capacitance consisting of inherent circuitcapacitance effectively across said terminal circuit, capacitanceconsisting of inherent circuit capacitance effectively coupling saidwindings in opposition to their transformer coupling, said capacitancesresonating with the resultant inductance of said transformer and saidterminal circuit at a frequency within said band at which such resonanceis undesired, and additional capacitance effectively in parallel withsaid capacitance across said terminal circuit and of such value assubstantially to balance out any irregularity in the couplingcharacteristics between said terminal circuit and said winding oi'greater inductance at frequencies in the vicinity of said particularfrequency of undesired resonance.

7. A signal-translating circuit for passing a signal comprising a bandof frequencies, said circuit comprising, a transformer havingcloselycoupled primary and secondary windings of substantially differentinductances, a terminal circuit connected with the one of said windingsof lower inductance, capacitance consisting of inherent circuitcapacitance effectively across said terminal circuit, capacitance.consisting of inherent circuit capacitance effectively coupling saidwindings in opposition to their transformer coupling, said capacitancestending to resonate with the resultant inductance of said transformerand said terminal circuit at a frequency within said band at which suchresonance is undesired, and additional capacitance effectively inparallel with said capacitance effectively coupling said windings inopposition to their transformer coupling and of such .value assubstantially to balance Vout any irregularity in the couplingcharacteristics between said terminal circuit and said winding ofgreater inductance at frequencies in the vicinity of said particularfrequency of undesired resonance.

8. A signal-translating circuit comprising, a. transformer havingclosely-coupled primary and secondary windings of substantiallydifferent inductances, said winding of greater inductance `having aself-inductance Liri-Lm, said winding of less inductance having aself-inductance Ln-l-Lm, and said primary and secondary windings havingmutual inductance Lm, a capacitance Cb effectively across said windingof less inductance, and a capacitance Cm effectively coupling saidwindings in opposition to said transformer coupling, where the circuitparameters are as defined in the specification. said capacita-ncesresonating with the resultant inductance of said transformer at afrequency at which such resonance is undesired, said inductancesand'capacitances being proportioned in accordance with the relation:

Ct L.,

whereby any irregularity in the coupling characteristics between saidterminal circuit and said winding of greater inductance at frequenciesin the vicinity of said frequency is substantially balanced out.

9. A signal-translating circuit comprising, a transformer havingclosely-coupled primary and secondary windings of substantiallydifferent inductances, said winding of greater inductance having aself-inductance Lu-l-Lm, said winding oi' less inductance havingaself-inductance Lb-l-Lm, and said primary and secondary windings havingmutual inductance Lm, a terminal circuit of inductance Le connected withsaid winding of less inductance, a capacitance Cb effectively acrosssaid terminal circuit, and a capacitance Cm eiectively coupling saidwindings in opposition to their transformer coupling, where the circuitparameters are as defined in the specification, said capacitancesresonating with the resultant inductance of said transformer and saidterminal circuit at a frequency at which .such resona-nce is undesired,and said inductances and capacitances being proportioned in accordancewith the relation:

whereby any irregularity in the coupling characteristics between saidterminal circuit and said winding of greater inductance at frequenciesin the vicinity of said frequency is substantially balanced out.

l0. A signal-translating circuit for passing a signal comprising a bandof frequencies, said circuit comprising, an autotransformer having aplurality of windings connected in series. a terminal circuit connectedwith those of said windings that are common to the primary and secondarycircuits of the transformer, capacitance effectively in parallel withsaid terminal circuit, and capacitance effectively in parallel with theothers of said windings. said capacitances resonating with the resultantinductance of said transformer and said terminal circuit at a frequencywithin said band at which such resonance is undesired, and saidcapacitances being relatively so proportioned with respect to saidinductances as substantially to balance out any irregularity in thecoupling characteristics between said terminal circuit and said othersof said windings at frequencies in the vicinity of said particularfrequency of undesired resonance.

ll. A signal-translating circuit for passing a signal comprising a bandof frequencies, said circuit cornprising, a transformer having separatebut closely-coupled primary and secondary windings of substantiallydifferent inductances, a terminal circuit connected with the one of saidwindings of lower inductance, capacitance eectively across said terminalcircuit, and capacitance e'ectively coupling said windings in oppositionto their transformer coupling, said capacitances resonating with theresultant inductance of said transformer and said terminal circuit at afrequency within said band at which such resonance is undesired, andsaid capacitances being relatively so proportioned with respect to saidinductances as substantially to balance out any irregularity in thecoupling characteristics between said terminal circuit and said windingof higher inductance at frequencies in the vicinity of said particularfrequency of undesired resonance.

HAROLD A. WHmlER

